Variations in the X-ray Sky

The All Sky Monitor (ASM) on board the Rossi X-ray Timing Explorer (RXTE) has been monitoring the X-ray emission from relatively bright cosmic X-ray sources since the launch of RXTE in February 1996. This monitoring represents the most detailed look at the time variability of cosmic X-ray sources. Using the All-Sky Monitor data, the ASM team has produced a movie showing in startling detail the extreme variation of the X-ray sky. Sources appear and disappear, some flicker mildly, others brighten wildly for a period of time and then fade away. The quicktime movie above shows a segment of this movie highlighting the X-ray antics of the Galactic "microquasar" 1915+105, visible on Aug 29, 1997 as a yellow circle on the left side of the screen. As time goes on the intensity of the source (represented by the size of the circle) and the energy of the emitted X-rays (represented by the color of the circle) change erratically. However, if we could show the movie in super-slow motion, we would see that the source pulses nearly 67 times every second. Note that the sources are displayed in Galactic coordinates (in which the center of the Milky Way is at center of the frame, and the disk of the Galaxy runs horizontally through the center). Most of the X-ray sources fall in the plane of our Galaxy; the brightest X-ray source, Scorpius X-1, is the large circle just above the Galactic center. The full movie is astonishing and available at the ASM web site at the Massachussetts Institute of Technology.

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Page Author: Dr. Michael F. Corcoran
Last modified June 14, 2001